A head mounted display (“HMD”) or head wearable display is a display device worn on or about the head. HMDs usually incorporate some sort of near-to-eye optical system to create a magnified virtual image placed between a meter or so (near) and optical infinity (distant) in front of the user. Single eye displays are referred to as monocular HMDs while dual eye displays are referred to as binocular HMDs. Some HMDs only permit the user to see a display image (e.g., computer generated image, still image, video image, etc.) while other types of HMDs are capable of superimposing the display image over a real-world view. The type of HMD that shows a real-world view combined with a display image typically includes some form of see-through eyepiece and can serve as the hardware platform for realizing augmented reality. With augmented reality the viewer's perception of the world has added to it an overlaying display image. This type of system is sometimes also referred to as a head-up display (“HUD”). Fully immersive displays (i.e., not see-through) are often referred to as virtual reality (“VR”) displays. Immersive HMDs can also provide augmented reality by electronically combining images from a camera or other sensors that are viewing the world in front of the user, fused with other electronic imagery or information.
HMDs have numerous practical and leisure applications. Aerospace applications permit pilots to see vital flight control information without taking their eyes from the flight path. Public safety applications include tactical displays of maps and thermal imaging. Other application fields include video games, transportation, and telecommunications. There are certain to be newly found practical and leisure applications as the technology evolves; however, many of these applications are limited due to the cost, size, weight, field of view, and efficiency of conventional optical systems used to implement existing HMDs.